Metal ingots, billets and other castparts are typically formed by a casting process which utilizes a vertically oriented mold situated above a large casting pit beneath the floor level of the metal casting facility, although this invention may also be utilized in horizontal molds. The lower component of the vertical casting mold is a starting block. When the casting process begins, the starting blocks are in their upward-most position and in the molds. As molten metal is poured into the mold bore or cavity and chilled (typically by water), the starting block is slowly lowered at a predetermined rate by a hydraulic cylinder or other device. As the starting block is lowered, solidified metal or aluminum emerges from the bottom of the mold and ingots, rounds or billets of various geometries are formed, which may also be referred to herein as castparts.
While the invention applies to the casting of metals in general, including without limitation aluminum, brass, lead, zinc, magnesium, copper, steel, etc., the examples given and preferred embodiment disclosed may be directed to aluminum, and therefore the term aluminum may be used throughout for consistency even though the invention applies more generally to metals. This type of casting wherein fluid (gas or liquid) is applied directly to an emerging castpart is generally referred to as direct chilled or direct cooled casting.
While there are numerous ways to achieve and configure a vertical casting arrangement, FIG. 1 illustrates one example. In FIG. 1, the vertical casting of aluminum generally occurs beneath the elevation level of the factory floor in a casting pit. Directly beneath the casting pit floor 101a is a caisson 103, in which the hydraulic cylinder barrel 102 for the hydraulic cylinder is placed.
As shown in FIG. 1, the components of the lower portion of a typical vertical aluminum casting apparatus, shown within a casting pit 101 and a caisson 103, are a hydraulic cylinder barrel 102, a ram 106, a mounting base housing 105, a platen 107 and a starting block base 108 (also referred to as a starting head or bottom block), all shown at elevations below the casting facility floor 104.
The mounting base housing 105 is mounted to the floor 101a of the casting pit 101, below which is the caisson 103. The caisson 103 is defined by its side walls 103b and its floor 103a. 
A typical mold table assembly 110 is also shown in FIG. 1, which can be tilted as shown by hydraulic cylinder 111 pushing mold table tilt arm 110a such that it pivots about point 112 and thereby raises and rotates the main casting frame assembly, as shown in FIG. 1. There are also mold table carriages which allow the mold table assemblies to be moved to and from the casting position above the casting pit.
FIG. 1 further shows the platen 107 and starting block base 108 partially descended into the casting pit 101 with ingot or castpart 113 being partially formed. Castpart 113 is on the starting block base 108, which may include a starting head or bottom block, which usually (but not always) sits on the starting block base 108, all of which is known in the art and need not therefore be shown or described in greater detail. While the term starting block is used for item 108, it should be noted that the terms bottom block and starting head are also used in the industry to refer to item 108, bottom block is typically used when an ingot is being cast and starting head when a billet is being cast.
While the starting block base 108 in FIG. 1 only shows one starting block 108 and pedestal 105, there are typically several of each mounted on each starting block base, which simultaneously cast billets, special shapes or ingots as the starting block is lowered during the casting process, as shown in later Figures and as is known.
When hydraulic fluid is introduced into the hydraulic cylinder at sufficient pressure, the ram 106, and consequently the starting block 108, are raised to the desired elevation start level for the casting process, which is when the starting blocks are within the mold table assembly 110.
The lowering of the starting block 108 is accomplished by metering the hydraulic fluid from the cylinder at a predetermined rate, thereby lowering the ram 106 and consequently the starting block at a predetermined and controlled rate. The mold is controllably cooled or chilled during the process to assist in the solidification of the emerging ingots or billets, typically using water cooling means.
There are numerous mold and casting technologies that fit into mold tables, and no one in particular is required to practice the various embodiments of this invention, since they are known by those of ordinary skill in the art.
Mold tables come in all sizes and configurations because there are numerous and differently sized and configured casting pits over which mold tables are placed. The needs and requirements for a mold table to fit a particular application therefore depends on numerous factors, some of which include the dimensions of the casting pit, the location(s) of the sources of water and the practices of the entity operating the pit.
The upper side of the typical mold table operatively connects to, or interacts with, the metal distribution system. The typical mold table also operatively connects to the molds which it houses.
When metal is cast using a continuous cast vertical mold, the molten metal is cooled in the mold and continuously emerges from the lower end of the mold as the starting block base is lowered. The emerging billet, ingot or other configuration is intended to be sufficiently solidified such that it maintains its desired shape. There is typically an air gap between the emerging solidified metal and the permeable ring wall. Below that, there is also a mold air cavity between the emerging solidified metal and the lower portion of the mold and related equipment.
Since the casting process generally utilizes fluids, including lubricants, there are conduits and/or piping designed to deliver the fluid to the desired locations around the mold cavity. Although the term lubricant will be used throughout this specification, it is understood that this also means fluids of all types, whether a lubricant or not, and may also include release agents.
Working in and around a casting pit and molten metal can be potentially dangerous and it is desired to continually find ways to increase safety and minimize the danger or accident potential to which operators of the equipment are exposed.
Butt curl is a known and undesired phenomena incurred during the casting of some metals and/or shapes, and is generally caused by the shrinking of some portions of the castpart relative to other portions. Excessive butt curl can result in breakout or bleedout situations in which molten metal escapes during the molding process and requires that the casting be immediately aborted. In casting shapes such as ingots, especially when casting metal alloys which have a lower thermal conductivity, there is a tendency for butt curl to occur more and to a higher degree. For instance, each of the alloys has a different liquidus to solidus region and a thermal conductivity. Some of these alloys, such as the ones which have higher magnesium contents, also have much lower thermal conductivities. As a result, it is more difficult to form a uniform water vapor barrier or film barrier. The center of these ingots tend to operate in nucleate boiling sooner than the rest of the ingot, which is not desirable.
It is desirable to maintain a higher metal temperature in the center surface portions of the ingot castpart to reduce temperature gradients and to reduce the incidence and/or magnitude of butt curling.
As one would expect with a well recognized problem, several attempts have been made to reduce the incidence and magnitude of butt curl. However the Applicant is not aware of any such attempts or solutions which also maintained a relatively constant flow rate through the various variable coolant discharge apertures. For instance one solution was to increase the cooling in the quarter portions by increasing the baffle and spray hole cross-sections in order to increase the cooling in those areas to reduce the gradient between those areas and the center surface portions. The increase in flow through the larger apertures in the quarter portions may result in other undesired effects.
The casting and cooling process leaves what those skilled in the art refer to as steam stains, which are patterns or stains on the exterior of the castpart from casting, and the higher the steam stain in any given portion of the castpart such as quarter portion or center surface portion from the bottom of the castpart, the longer that portion remained at a higher temperature. In casting ingots as one example, it is therefore desired to have a steam stain pattern in which the steam stains are higher in the center surface portions (a fractional portion) of the castpart than toward the ends or in what is referred to as the quarter portions. In casting other shapes, it may be desired to have one steam stain in a first fractional surface location, and a second steam stain pattern in a second fractional surface location. In fact there several different steam stain patterns or heights may be desired for one particular castpart and this invention provides the ability to accomplish this.
In one aspect of the invention, it is an object to provide an improved cooling system for certain shaped castparts or for certain metal or alloy compositions.
It is an object of some embodiments of this invention to provide a cooling system which leaves a steam stain which is higher in magnitude, or runs higher up the castpart, in the center surface portions than in the end or quarter portions.
It is an object of some embodiments of this invention to provide a cooling and casting system which reduces butt curl, even for relatively low thermally conduct metal alloys.